The invention concerns a machine for manufacturing helically-seamed tubing from a strip-like profiled blank, in which machine the strip-like profiled blank is guided to travel under positive guidance into a tubular shape over a distance corresponding to the pitch of a helical seam, whereupon the adjacent edges of the profiled blank brought into jointing contact are seamed together by using at least two seaming rolls, one of which is inside the tube being formed and the other outside it, and in which machine the positive guidance of the profiled blank into a helical shape is accomplished from the outside thereof by a loop, adjustable in size and formed of a chain-type traction member, inside which loop the strip-like profiled blank is adapted to be positively fed, in which one end of the traction member constituting the loop is attached to a rocker.
A number of different machines operating on different principles are previously known by means of which helically-seamed tubing can be produced. The most prevalent machines are of the kind in which a pre-profiled metal strip is fed upon a cylindrical mandrel piece and the finishing of a seam is then accomplished by means of various kinds of seaming rolls. In these prior art machines the axis of the mandrel forms a given angle with the pre-profiled strip, the magnitude of which angle is mainly determined as a function of the strip width employed and the inside diameter of the tubing to be manufactured.
In other previously-known types of machine a mandrel or equivalent workpiece is not used, but, instead, a pre-profiled strip is positively fed into a stationary shaped piece which conforms to the external shape of tubing and incorporates contact surfaces. When advancing along the contact surfaces, the pre-profiled strip is forced to bend into a tubular shape, and the seam ends are brought into contact with each other and seamed to form a finished seam by means of rotating seaming rolls.
Among the drawbacks of previously-known machines is that in their storage inventory a large number of different tool units have to be stored, which have to be replaced each time that the strip width or type used is changed to another or when the diameter of the tubing to be made changes. Such tool units are difficult to manufacture and their manufacturing is quite expensive, which implies that in versatile production a considerable amount of capital has to be tied up in them. On the other hand, they tend to wear down, because, when gliding along the guiding surfaces provided in them, the tubing being formed wears them down at a relatively fast rate, which very soon leads, among other things, to the fact that the actual measured tolerances and the appropriate tolerances in view of quality change in an unfavorable direction, and the quality of the tubing, e.g., the tightness of the helical seam, deteriorates.
A previously-know apparatus for solving the above-mentioned problems is disclosed in FI Pat. No. 45 418. The machine of this prior art apparatus chiefly belongs to the latter group of the above-mentioned machine types. In this prior art apparatus, adjustment of an outside diameter of the tubing to be helically seamed is achieved by means of a flexible traction member.